A star that astronomer Edwin Hubble viewed 100 years ago this month changed our concept of the universe. The star, M31-V1, changes brightness in a regular pattern that astronomers can use to calculate the star's distance. Hubble's observations (at lower right, with M31-V1 labeled "var") demonstrated that the star's home, the starry disk known as M31, was a separate galaxy and not a mote of matter within the Milky Way Galaxy. That proved that there are myriad galaxies in the universe, greatly expanding its known size. The main image shows M31-V1's location within M31 (the Andromeda Galaxy), while the image at top right shows a close-up of the star and its busy neighborhood. [NASA/ESA/Hubble Heritage Team]